Simona Kaftanová

1. Immunoglobulins - structure.Immunoglobulins - function.Genetic background of immunoglobulin production.Biological and chemical characteristics of immunoglobulin classes IgG and IgA.Biological and chemical characteristics of immunoglobulin classes IgM, IgD and IgE.Isotype switching. Idiotypes and anti-idiotypes - their role. Immunological memory.Ontogenesis of the immune response.Primary immune response.Secondary immune response .Effector functions of immunoglobulins. Simona Kaftanová

2. The structure of immunoglobulins 4 polypeptid chains: 2 identical heavy chains (H) 2 identical light chains (L) H chains:μ, δ, γ, α, ε L chains: κ, λ Izotypys = classes of antibodies : IgM (μ) IgD (δ) IgG (γ) IgA (α) IgE (ε)

3. The structure of immunoglobulins Ig fragments produced by proteolytic digestion (papain): • Fab fragments (portions) contain the antigen binding sites of the antibody • Fc fragment binds to cells through Fc-receptor Domains: • domains of V regionsforma recognizing unit for Ag • domains of C regionsdetermine secondary biological functions of antibody

4. The structure of immunoglobulins Paratop - the binding site for Ag (for it’sepitop ) = part of Ig made of hypervariable regions of VH and VL (hypervariableregion – spike of variable region with hypervariable loops of aminoacid (AA) sequences; the binding site specificity is determined by AA sequences and both by morphology and shape of the loop) Idiotop – individual and rarely structureslocalized in the variable region; some of them are identical with the binding site, some lie except of the paratop Idiotyp - the sum of idiotopes of an Ig molecule

5. Anti-idiotypic antibodies • antibodies of the 2nd generation (idiotyp of the 1st gen. of antibodies looks like an antigen, idiotyp can start production of Abb against itself – antiidiotypic antibodies) • in principle reflect the antigen • other new antibodies (3rd generation) are produced against them → antiantiidiotypic antibodies → idiotypic net • regulatory function idiotyp of the 1st generat. of antibodies antibodies of the 2nd generation antibodies of the 3rd generation epitops

6. Function of Igg • antibodies – solubil Igg • antigen receptor (BCR) – (IgM a IgD on the surface of B cells) • differences in H chain structure (Fc ftagment) determine secondarybiological function of antibodies: biological half life, distribution in the body, passing through the placenta,complement activation, binding to cells through Fc-receptor – opsonization, IgE binding on mastocytes etc.

8. Genetic basis of Ig production H chains genes(chromosome 14) • genes are structured in V, D, J, Csegments (segments contain more regions compared with L chains) • V („variability“, several hundred) • D (cca 50) • J (9) • C (encoding izotypes - Cμ, Cγ, Cα, Cδ, Cε) L chains genes (κ – chromosome 2, λ – chromosome 22) • less complicated • V, J, C segments

9. H chain recombination: a) D-J rearrangement - accidental D-J joiningb) V-D rearrangement – V-D-J joiningc) transcription if V-D-J product is readable, then splicing (V-D-J-C joining)d) translation in protein (H chain)

10. L chain recombination : V-J rearrangement transcription splicing –VJC rearrangement

12. Mechanisms contributing to antibody diversity: • chance recombinations • imprecise joining of V, D, J genes • extensive mutations involving variable-region genes after antigen exposure

13. Isotypeswitching • during the immune response, plasma cells switch from producing IgM to IgG or to another Ig class (IgA, IgE) • mechanism: segment Cμ is excluded and replaced by other next segment f.e. Cγ (IgG production) • regulation – mainly IL-4 • change only in the H-chain constant domains (CH); no change in antigen-binding specificity

14. Humoral immune response Primary immune response(reaction against primary infection): • 2 periods: primary, secondary • characteristic: memory cells, production antibodies with the increasing affinity to Ag Primary period of primary immune response: • the first Ag exposure (secondary lymf. org.) → …see Th2 based immune reaction… • clonal expansion of B cell with identical or similar specifity to Ag → diferenciation to plasmocytes and memory cells • some of plasmocytes back to circulation (bone marrow,...) • in 3-4 days secretion plenty of IgM with low affinity to Ag • imunokomplexes are displayed by FDC (folicular dendritic cells in secondary lymf. org.) Exception: T-independent Ag– antibody production is induced directly, without the involvement of T helper cells; typically polysaccharides, lipids

15. Secondary period of primary immune response : • affinity maturation: the antigen displayed by FDC is recognized by B cells → other proliferation a diferenciation of B lymfo → their Ig V genes undergo extensive somatic mutations → changes of Ig binding sites (hypervariability parts) → competition about lower amount of Ag → B cells that recognize the antigen with the highest affinity are selected to survive b) isotype switching: start of production other Ig which is on (mainly IgG, others IgA, IgE, IgD)) After primary immune response Abb circulate in organism for a certain time; they stop reinfection for a certain time.

16. Secondary immune response (reaction against repeatedly infection): • activation of memory cells • increasing of the affinity maturation (production of antibodies with increased affinity to Ag) • continuation of isotype switching (higher amount of antibodies is produced; start of Ig production is faster (faster and higher amount of IgG) • suppression of infection is quicker and more effectively

17. Effector functions of immunoglobulins • neutralization – Igg bind a blocade critical epitops of toxins, virus and other microorganisms • inhibition of patogen adherence – IgA blocade adherence of microorganisms on the mucose surface • opsonization – Ig is binded on Ag; fagocytes are more able to swallow up Ag (FcR on the fagocytes surface) • ADCC (antibody-dependent cell-mediated cytotoxicity) – IgG is binded on Ag; FcR for IgG on the NK cells surface; binding IgG and FcR is a stimul for NK degranulation on Ag (cytotoxic products) • complement activation via classical pathway → products of complement...

18. Ontogenesis of immune response a/ prenatal • Hematopoesis – extraembryonaly (start in the week 2-3 of gestation) → then in liver (whole prenatal period) → postnataly bone marrow (the main organ of hematopoesis) • T-cells - precursors to thymus → diferenciation in lymfoid cells, selection. • B-cells – synthesis interauter. IgM unable to detection (detectable concentration IgM = information about IU infection) x IgG production starts after the birth • monocytes-makrophages – mature already in foetus • neutrophils – smaller amount

19. Ontogenesis of immune response b/ postnatal B lymfo: • mainly IgM production immediately after the birth (adult conc. between the year 1.- 3.) • IgG production increases slow (and decrease of mothernal IgG) → the most decrease between the month 3. – 6. • humoral response to polysacharide antigen (f.e. Haemophilus) arises by the age of 2 yr. T lymfo : • lower activity after the birth Innate imunity: • lower ability of the function

20. Ontogenesis of immune response c/ old age • decreased cytotoxicity of NK-cells and macrophages • decreased resistance against viral infections, decreased anti-tumour immunity • switching from Th1 to Th2 (weaker humoral response under new stimuli but increased production of autoantibodies)